This application claims priority under 35 U.S.C. xc2xa7xc2xa7119 and/or 365 to 11-190042 filed in JAPAN on Jul. 5, 1999; the entire content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an indicating method for visualizing and indicating measurement data, and particularly relates to a characteristics indicating method capable of visualizing the characteristics of a measured object from various types of measurement data measured for a rotating apparatus such as motors or turbines or the like, or non-rotating vibrating apparatus such as smokestacks or automobiles or the like, thereby enabling identification of the source of stimulus and estimation of the cause of abnormalities and vibrations.
2. Description of the Related Art
Spindle motors for rotating a disk-shaped recording medium are required to rotate at high speed, and at the same time, due to an increase of required data storage capacity, the motors are required to assume high precision of rotation, e.g. decrease vibration components asynchronous with the rotation such as the Non-Repeatable Run Out (NRRO). Vibrations and noise caused by the asynchronous components of the vibration frequency of the motor become large due to resonance phenomena occurring when a natural vibration frequency of the motor is the same or about the same as an excitation frequency occurring at the bearing when the motor rotates. Particularly, in hard disk drives, not only vibrations and noise are increased by resonance, but also NRRO is increased thereby causing servo track errors. Accordingly, spindle motors for hard disk drives are required to be free from the above-described resonance, and low in NRRO at rated rotations.
The excitation frequency of the bearing is a vibration frequency which occurs due to machining tolerance, warping, or the like, of the bearing components including the inner race, outer race, balls, and retainer. Resonance is generated in the event that the vibration frequency corresponds with the natural frequency of the motor.
In order to avoid the above-described resonance phenomena, the resonance phenomena was conventionally detected with the phenomena being visualized and indicated in accordance with the measured data such as vibrations and the like of the motor. As an example, FIG. 4 shows the vibration frequencies of a spindle motor visualized and indicated by a waterfall diagram. The waterfall diagram is a three-dimensional representation for indicating spectral waveforms of frequencies of vibration with the horizontal axis representing the frequencies, the vertical axis representing amplitude of vibration, and the depth-wise axis representing the number of rotations. The frequencies of vibration is obtained by steps of: measuring the vibrations generated by the spindle motor or the housing of the hard disk drive containing the spindle motor synchronously with change in rotations; subjecting the measured vibrations to amplification processing; and subjecting the frequencies of the measured vibrations to spectral analysis by using a FFT (fast Fourier transform) analyzer.
Presentation by the waterfall diagram visually indicates natural frequency characteristics of an object to be measured, e.g. a motor, such as at which frequency the vibration or amplitude peak of the measurement object is, the magnitude of vibration or amplitude peak values, how the vibration amplitude peak changes along with changes in rotations, and so forth.
On the other hand, in recent years, Campbell diagrams are coming into use for analysis of such resonance phenomena. As shown in FIG. 5, a Campbell diagram is a graph with the horizontal axis representing the motor rotations and the vertical axis representing the frequency, and can be considered to be a two-dimensional representation of the waterfall diagram shown in FIG. 4. In the Campbell diagram shown in FIG. 5, the amplitude of vibrations is represented by the diameter of the circles. Note that in FIG. 5, fr represents rotational frequency of the motor.
The waterfall diagram indicates change in vibrations according to rotational speed of a rotating apparatus, change in frequency components with time, change in natural frequencies due to temperature or the like. However, a Campbell diagram as shown in FIG. 5 is used to indicate such characteristics when it is required to identify the phenomena in a more precise manner.
However, when the conventional Campbell diagram indicates such vibration characteristics, the diagram includes graphic representation of all components of the measured data. Therefore, the excitation frequency of the bearing and components having far greater amplitude than the excitation frequency are indicated on the graph all together. In the present context, components considered to be xe2x80x9cfar greaterxe2x80x9d are those components which are significantly larger (e.g., as much as an order of magnitude, or more, larger), so as to overwhelm the remaining components. That is, it is difficult or impossible to discern a component when there is a far greater component at the same frequency. Accordingly, only the components with the very great amplitudes were visible, making it impossible to analyze and identify the vibration generating mechanism in order to identify the cause of abnormalities.
It is an object of the present invention to provide a characteristics indicating method which enables precise grasping of a phenomena from measured data, and also enables estimation of locations and modes of abnormalities.
The characteristics indicating method according to the present invention is for visually indicating vibration measurement data of a physical quantities or parameters such as displacement, speed, acceleration, sound pressure or the like from a measured object such as a rotating apparatus or vibrating apparatus, wherein specific components or parameters of the measurements are removed from the measurement data or minimized therein, and indicated in a Campbell diagram.
The characteristics indicating method of the present invention may be used to measure a rotating apparatus, including, for example, motors, turbines, or the like. The method of the present invention may also be used to measure a non-rotating vibrating apparatus, such as a smokestack, automobile, or the like. Slight asynchronous vibrations in the vibrations generated by the measured object while it is operating, can be visualized by removing or minimizing specific components or parameters having amplitudes far greater than those of the components to be indicated.
In an exemplary embodiment of the present invention for visualizing vibration, related measurement data generated by the measured object in operation having specific components with amplitudes far greater than those of the components to be indicated are removed or minimized. Such related measurement data may include, for example, data pertaining to the displacement, speed, acceleration, sound pressure, or the like, of the measured object. This enables a representation to be made on a Campbell diagram with amplitudes being represented by, for example, the size of circles centered on corresponding coordinates, one axis of which representing vibration frequencies and the other axis representing a physical quantity such as operating frequencies, time, temperature, or the like. In this way, the vibration state of the vibrating apparatus may be ascertained to more properly represent how the vibration varies with changes in operating frequencies, time, temperature, or the like.
In the event that the measured object is a motor having a rotor which is a principal moving part thereof and is rotatably supported by a stationary member via a ball bearing, indication is made by a Campbell diagram with one axis representing the vibration frequencies, the other representing rotor rotation. The size of figures such as circles centered on corresponding coordinates may be chosen to represent the amplitude. In accordance with this exemplary embodiment, the shapes are not necessarily circles but may be polygons such as triangles or quadrangles. Thus, the excitation source and resonance phenomena can be manifested in a more appropriately by the size of the figures. This provides an indication for grasping the resonance phenomena due to the correspondence of the bearing excitation frequency with the natural frequency.
One exemplary embodiment of the present invention involves removing or minimizing specific components of the measurement data having amplitudes far greater than those of the components to be indicated, indicating the measured data on a Campbell diagram, and superimposing excitation frequencies capable of generating vibration components at the bearing. This enables the identification of the excitation source. Also, if enlarged indication is made by amplifying the vibration frequency at the time of making the Campbell diagram indication, confirmation of the resonance phenomena can be easily made. Moreover, the types of lines and/or color or the like may be changed in accordance with the direction of vibration, vibration characteristics, or the like, for indication on figures such as circles. This allows identification of excitation frequencies of the bearing, or the like, to be indicated effectively, and identification of the characteristics of vibrations.